The present invention relates to an injection device for a plunger-type injection molding machine which injects a molten resin by means of an injection plunger. More specifically, the present invention relates to an injection device for a plunger-type injection molding machine equipped with a resin ejection opening, which reliably ejects the resin which, during the injection operation, has leaked out of the injection chamber to the area around the injection plunger shaft, from the rear edge of the injection cylinder.
Plunger-type injection molding machines supply molten molding resin to an injection device, and inject it into a molding die with an injection plunger. In practice, plunger-type injection molding machines are frequently used as a screw preplasticizing injection molding machine; therefore the explanation below refers to a screw preplasticizing injection molding machine.
A conventional screw preplasticizing injection molding machine contains a plasticizing screw within a plasticizing chamber in a plasticizing section; an injection plunger is contained within an injection chamber in an injection section, and a connecting path is provided between the plasticizing section and the injection section which connects the plasticizing chamber and the injection chamber. A synthetic resin material (hereinafter xe2x80x9cresinxe2x80x9d) supplied from a hopper is blended and melted, which is to say plasticized, within the plasticizing chamber by means of the rotation of a plasticizing screw and the heat of the plasticizing chamber, and is pressure fed to the injection chamber through the connecting path. At this point, the stoke of retraction of the injection plunger which retracts with the pressure feed is detected, and the amount of molten resin is measured (metered). Next, the injection plunger advances, and the molten resin is injected into a cavity in the die.
In such a plunger-type injection molding machine, in order to ensure that the injection plunger does not bite into the injection cylinder during injection, a minute gap exists between the plunger head and the injection cylinder inner wall. Also, the injection plunger shaft has a slightly smaller diameter than the injection plunger head, and a step is formed between the plunger head and the plunger shaft. Therefore, during the injection operation, in which molten resin is filled at high pressure into a die, an extremely small amount of molten resin leaks out of the gap between the plunger head and the injection cylinder inner wall and accumulates in the gap between the plunger shaft and the injection cylinder inner wall. Resin which thus leaks out (hereinafter xe2x80x9cleaked resinxe2x80x9d) is pressed into the aforementioned step with each retraction of the plunger head and is pushed backward, such that it is continuously ejected from the rear (base) portion of the injection cylinder, or from a resin ejection opening provided near the rear edge of the injection cylinder. However, when this leaked resin has not been perfectly ejected, the leaked resin is further compressed with each injection by the leaked resin, forming a dam, and the retraction of the injection plunger is prevented, thus impeding the metering operation.
Several injection devices equipped with resin ejection openings with which the leaked resin could be ejected outside the injection cylinder have thus been proposed. For example, Jpn. Patent H8-156049 discloses an injection device equipped with a scraper ring, which supports an injection plunger as well as scrapes off ejected resin which has adhered and emerged around the injection plunger shaft. In Jpn. Patent H8-229997, an injection cylinder is proposed in which, in order to eject the leaked resin in the molten resin state, a resin drain opening is provided directly on the injection cylinder, while at the same time a heater is added to the injection cylinder behind that drain opening. Jpn. Patent H9-85787 proposes, in addition to the structure of Jpn. Patent H8-229997, an injection device which provides a scraping sleeve immediately behind the resin drain, such that the molten resin is prevented from leaking out behind the scraping sleeve.
When molding is performed with a general use resin, such resin is thermally stable, and there is therefore no degradation even if the leaked resin is exposed over long periods to high temperatures around the plunger shaft. Therefore, if molding can be carried out while maintaining a molding temperature sufficiently above the temperature at which resin begins to melt, the leaked resin will be ejected in the molten state from the injection cylinder, and will fall from the ejection opening in the molten state.
However, depending on the type of resin used, or even with the same resin, depending on molding conditions, leaked resin is ejected in many different forms.
For example, there are many types of engineering plastics or super engineering plastic materials with narrow stable-melting molding temperature, which are easily heat decomposed; these resins are usually molded at temperture just above the lower molding temperature limit. When 2 types of plastic materials having differing melting temperatures are mixed and used as an alloy in order to improve the strength of molded products, the molding temperature is adjusted to the lower limit molding temperature of the resin having the higher molding temperature, in order to prevent degradation of the resin having the lower molding temperature. In such cases, when the molding temperature falls somewhat below the lower limit temperature, the viscosity of the molten resin can increase, or internal hardening may occur. Under such circumstances leaked resin may readily harden around the ejection opening, where the temperature can easily drop.
When imparting flame resistance or other characteristics to a resin by admixture of additives to the resin, the molten resin may become more easily thermally degraded. When molding with an extremely small injection quantity per cycle, the length of the stroke which the injection plunger moves for a molding is extremely small compared to the total motion stroke inherent to the molding machine, and the leaked resin is exposed to high temperatures around the plunger shaft for a long period before being ejected, making it prone to thermal degradation. In such cases, as well, the molten resin viscosity increases, and the resin is prone to internal hardening.
When changing materials from a high molding temperature resin to a low molding temperature resin, lowering the injection cylinder heater temperature setting from high to low temperature before the pre-changeover leaked resin has been completely ejected from the ejection opening will result in a lowered temperature at the ejection opening, such that leaked resin will harden and not fall down at the ejection opening. To avoid this, it was previously necessary to sufficiently purge until the leaked resin had been completely ejected, maintaining the injection cylinder temperature setting at the pre-changeover high temperature, requiring extra time to be added to the purging operation.
An object of the present invention is to provide an injection device which will drop the leaked resin such that it does not plug up the ejection opening even when the resin is in one of the various states described above, whereby it is prone to plug up the ejection opening. Therefore, for resin capable of being ejected in the molten state, an injection device equipped with an ejection guide capable of controlling temperature independently from that of the injection cylinder is provided in order to enable reliable ejection in the molten state. For resins prone to hardening, an injection device is provided which is equipped with an ejection guide capable of ejecting the resin by dividing it into fine strands, as well as independently controlling temperature. The above ejection guides may also be made selectively detachable/attachable in response to the resin ejection state.
A plunger-type injection molding machine injection device is provided, wherein molten resin in an injection cylinder injection chamber is injected by means of an injection plunger, the device including an ejection guide. The ejection guide having a cylindrical portion with a diameter smaller than the outside diameter of the rear edge of said injection cylinder, a flange portion, and a guide hole penetrated by an injection plunger shaft. The ejection guide including a resin ejection opening in said flange portion contacting said injection cylinder at said cylindrical portion, and being equipped at said cylindrical portion with a heating means by which temperature of said ejection guide is controlled independently of said injection cylinder, wherein the inside diameter of said guide hole on the front side of said resin ejection opening being formed so as to be approximately equal to or somewhat larger than the inside diameter of said injection cylinder, and the inside diameter of said guide hole on the rear side of said resin ejection opening being dimensioned so as to form a minute gap relative to the outside diameter of said injection plunger shaft.
By this construction the heating means controls the ejection guide temperature independently of the injection cylinder; control is executed such that leaked resin is definitively melted until it is ejected and falls from the ejection guide ejection opening. The leaked resin is ejected in a molten state, and is therefore preferable for injection devices which mold general purpose resins which are thermally stable.
Also, in another form of the plunger-type injection molding machine injection device of the present invention, a plunger-type injection molding machine injection device, in which molten resin in an injection cylinder injection chamber is injected by means of an injection plunger, includes an ejection guide having a cylindrical portion with a diameter smaller than the outside diameter of the rear edge of said injection cylinder, a flange portion, and a guide hole penetrated by an injection plunger shaft. The ejection guide contacting said injection cylinder at said cylindrical portion, said ejection guide being equipped at said cylindrical portion with a heating means by which temperature of said ejection guide is controlled independently of said injection cylinder; and a connecting piece for connecting said injection cylinder to an injection drive mechanism housing, said connecting piece having a drop opening on the bottom side thereof, wherein said ejection guide being further formed such that the inside diameter of the front side of said guide hole is approximately equal to or somewhat larger than the inside diameter of said injection cylinder, and the inside diameter of the rear side of said guide hole being formed into a cylindrical surface and dimensioned to form a minute gap relative to said plunger shaft with multiple ejection channels formed on said cylindrical surface parallel to the axis thereof.
By this construction, the heating means controls the temperature of the ejection guide independently of that of the injection cylinder. Temperature is controlled such that the fluidity of the leaked resin is maintained when the resin is in the guide hole of the ejection guide, and to the point that the leaked resin is divided into fine strands just as it is being ejected from the ejection channel. These strands harden without adhering to one another. The ejected leaked resin spreads out radially around the plunger shaft in the fine strand state and is suspended within a drop opening, finally breaking off and falling with the retraction of the plunger. This is preferable when using materials such as engineering plastics or super engineering plastics, where the molding temperature is controlled within a narrow range, or when using resin with an admixture of additives, or when molding an extremely small injection quantity per cycle.
In a plunger-type injection molding machine injection device according to yet another embodiment of the present invention, a plunger-type injection molding machine injection device, in which molten resin in an injection cylinder injection chamber is injected by means of an injection plunger, includes first and second ejection guides being attached interchangeably at a rear edge of said injection cylinder with a flange portion fastened by screws. The first ejection guide comprises an ejection guide having a cylindrical portion with a diameter smaller than the outside diameter of the rear edge of said injection cylinder, a flange portion, and a guide hole penetrated by an injection plunger shaft, said ejection guide including a resin ejection opening in said flange portion contacting said injection cylinder at said cylindrical portion, and said ejection guide being equipped at said cylindrical portion with a heating means by which temperature of said ejection guide is controlled independently of said injection cylinder, wherein the inside diameter of said guide hole on the front side of said resin ejection opening being formed so as to be approximately equal to or somewhat larger than the inside diameter of said injection cylinder, and the inside diameter of said guide hole on the rear side of said resin ejection opening being dimensioned so as to form a minute gap relative to the outside diameter of said injection plunger shaft. The second ejection guide comprises an ejection guide having a cylindrical portion with a diameter smaller than the outside diameter of the rear edge of said injection cylinder, a flange portion, and a guide hole penetrated by an injection plunger shaft, said ejection guide contacting said injection cylinder at said cylindrical portion, and said ejection guide being equipped at said cylindrical portion with a heating means by which temperature of said ejection guide is controlled independently of said injection cylinder; and a connecting piece for connecting said injection cylinder to an injection drive mechanism housing, said connecting piece having a drop opening on the bottom side thereof; wherein said ejection guide being further formed such that the inside diameter of the front side of said guide hole is approximately equal to or somewhat larger than the inside diameter of said injection cylinder, and the inside diameter of the rear side of said guide hole being formed into a cylindrical surface and dimensioned to form a minute gap relative to said plunger shaft with multiple ejection channels formed on said cylindrical surface parallel to the axis thereof.
There are at least two types of ejection guides, characterized by being interchangeable on the injection device.
Using this structure, either of the above ejection guides may be easily installed on the injection device. One of the ejection guides ejects the leaked resin in its molten state and causes it to drop, while the other ejection guide cuts the leaked resin into fine strands, ejecting it in a hard state and causing it to drop. Therefore, depending on the type of resin being molded, or even using the same resin, depending on molding conditions, it is possible to reliably eject the leaked resin in various states from the resin ejection opening and cause it to fall by installing one of the above ejection guides.
In the injection device for the plunger-type injection molding, in addition to the heating means, it is preferred that the temperature of the ejection guide is also controlled by a cooling means.
Preferably, the ejection guide is temperature controlled by a cooling means as well as by said heating means, said cooling means cooling a rear end of said flange portion with one of a nozzle or a cooling water pipe and said heating means heating said cylindrical portion with a heater.
In cases in which such a construction is adopted with respect to an ejection guide which causes the leaked resin to be ejected in the molten state, the cooling means makes it possible, depending on ejection conditions, to reliably prevent the molten resin which has been ejected from the resin ejection opening from passing through the gap between the guide hole on the rear wall of the resin ejection opening and the plunger shaft, and further leaking out to the rear. Also, when a structure such as this is adopted with respect to an ejection guide with which the leaked resin is cut into fine strands and hardens, is ejected, and falls, a cooling means can cool the fine strand resin ejected from the ejection channel such that it reliably hardens.
In a plunger-type injection molding machine injection device according to yet another embodiment of the present invention, a plunger-type injection molding machine injection device, in which molten resin in an injection cylinder injection chamber is injected by means of an injection plunger, includes an ejection guide at the rear edge of said injection cylinder; a connecting piece for connecting said injection cylinder to an injection drive mechanism housing; and a coupling for connecting said injection plunger to a linkage rod of an injection hydraulic cylinder. The connecting piece has a drop opening on the bottom side thereof, said coupling having a tapered surface on the front surface thereof; said ejection guide having a cylindrical portion with a diameter smaller than the outside diameter of the rear edge of said injection cylinder, a flange portion, and a guide hole penetrated by the said injection plunger shaft; said ejection guide contacting said injection cylinder at said cylindrical portion and being equipped at said cylindrical portion with a heating means by which temperature of said ejection guide is controlled independently of said injection cylinder; said ejection guide being further formed such that the inside diameter of the front side of said guide hole is approximately equal to or somewhat larger than the inside diameter of said injection cylinder, and the inside diameter of the rear side of said guide hole being formed into a cylindrical surface and dimensioned to form a minute gap relative to said injection plunger shaft with multiple ejection channels formed on said cylindrical surface parallel to the axis thereof.
In the injection device of the plunger-type injection molding machine, the injection cylinder is preferably connected through an insulating material at a small diameter cylindrical portion thereof to a housing for a drive means which drives the injection plunger; the ejection guide preferably includes a cylindrical portion with a smaller diameter than the outer diameter of the injection cylinder rear portion small diameter tube, connected to the small diameter cylindrical portion of the injection cylinder at the small diameter tube. this construction makes it unlikely that the temperature of the injection cylinder small diameter cylindrical portion will be directly or indirectly affected by the temperature of the injection cylinder main body. Furthermore, the ejection guide temperature is virtually unaffected by the temperature of the injection cylinder main body.